Book/Report

FZJ-2018-02826

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Transport through dissipative trapped electron mode and toroidal ion temperature gradient mode in TEXTOR

Rogister, A.FZJ* ; Hasselberg, F.FZJ* ; Waelbroeck, J.FZJ* ; Weiland, J.

1987
Kernforschungsanlage Jülich, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/18446

Report No.: Juel-2173

Abstract: A self-consistent transport code is used to evaluate how plasma confinement in tokamaks is influenced by the microturbulent fields which are excited by the dissipative trapped electron (DTE) instability . As shown previously, the saturation theory on which the code is based has been developed from first principles. The toroidal coupling resulting from the ion magnetic drifts is neglected; arguments are presented to justify this approximation. The numerical results reproduce well the neo-Alcator scaling law observed experimentally - e. g. in TEXTOR - in non detached ohmic discharges, the confinement degradation which results when auxiliary heating is applied, as well as a large number of other experimental observations. We also assess the possible impact of the toroidal ion temperature gradient ($\eta_{i}$) mode on energy confinement by estimating the ion thermal flux with the help of the mixing length approximation. We compare and analyse the temperature and density profiles measured in TEXTOR (q$_{a}$ $\simeq$ 2.45), at either variable mean density or variable additional power and check their stability against DTE and $\eta_{i}$ modes using, in the later case, a new criterion valid for arbitrary curvature. All profiles examined are marginally unstable against both modes, essentially between the q=1 and q=2 magnetic surfaces. The code results and the stability analysis lead to the following conclusions and suggestions: (1) the DTE instability suffices to explain the anomalous electron heat transport in low density discharges (attached plasmas) with or without additional heating; the marginal instability for the DTE mode thus follows from heat fluxes constraints; (2) the simultaneous marginal instability against the $\eta_{i}$ mode must then follow from particle fluxes constraints; (3) the conditions that both $\gamma_{\eta_1}$ and $\gamma_{DTE}$ ($\gamma$ = growth rate) must be small are consequently probably the restrictions which determine the profiles corresponding to each experimental condition and, to a large extent, profile consistency; (4) we suggest finally that the deviation from neo-Alcator scaling, the density limit, and the phenomenon of plasma detachment are interrelated effects which arise at high densities when the constraint on the electron heat flux becomes crucial.

---

Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

---

Database coverage:

---